The Federal Aviation Administration cleared the airport for flights when pilots can expect to see at least 1,800 feet down a runway. Previously, when the trees were in place, the FAA required a minimum "runway visual range" of at least 4,000 feet at the airport, according to airport owner and operator Massachusetts Port Authority.

With about $900,000 in funding mostly provided by the FAA, Massport has cleared about 80 of the airport's 1,300 acres over the last two years, said Airport Director Andrew B. Davis. The clearing took place mostly in Leicester near the western end of a runway designated for low-visibility landings, Mr. Davis said.

"What it does is allow commercial airplanes to land in lower-visibility conditions," Mr. Davis said.

Worcester Regional Airport sits about 1,000 feet above sea level, atop a hill on the city's western edge, and sometimes becomes wrapped in fog and low clouds. In addition to prohibiting flights when the runway visual range falls below 1,800 feet, the FAA also prohibits flights at the airport when the cloud cover sinks too low.

The only commercial air carrier providing service at the airport, JetBlue Airways Corp., canceled 11 flights and diverted eight others over the last two months because of low-visibility weather, according to JetBlue records. With four flights a day at the airport, that represented about 9 percent of JetBlue's traffic in Worcester.

If the new FAA standard had been in place earlier, fewer of those JetBlue flights would have been canceled or diverted, Massport said.

"We applaud Massport's plans to enhance the airport's navigation systems, and look forward to continue working with them and the airport so the service we provide is as reliable as possible for our customers," Bryan Baldwin, a JetBlue spokesman, said in an email.

Contact Lisa Eckelbecker at leckelbecker@telegram.com. Follow her on Twitter @LisaEckelbecker.